1. Field of the Invention
This invention relates to a combustion state detection apparatus for an internal combustion engine for detecting at least a misfire of the internal combustion engine and occurrence of knocking by detecting a change in the amount of ion caused by combustion in the internal combustion engine.
2. Description of the Related Art
With regard to a combustion state detection apparatus for an internal combustion engine according to the related art, a revolution change type misfire detection function for detecting a change in the number of revolutions of the internal combustion engine at the time of a misfire by a sensor has been proposed in order to detect continuous misfires and warn an operator of the internal combustion engine.
Also, a combustion state detection apparatus for an internal combustion engine using an ion current indicates excellent misfire detectability even in a multiple cylinder engine in which misfire detection accuracy drops in the revolution change type, and can detect a misfire every cylinder. The combustion state detection apparatus using ion current has variously been proposed.
In an apparatus described in JP-A-Hei.10-231772, the fact that a determination of a combustion state (presence or absence of misfire) of an internal combustion engine is made by an ion current is indicated.
FIG. 1 is a block diagram schematically showing a combustion state detection apparatus for an internal combustion engine according to the related art.
An example according to the related art will be described below on the basis of this block diagram. A system shown in FIG. 1 shows the case of performing high voltage distribution through a distributor 7 with respect to spark plugs 8a to 8d of each cylinder.
First, an ECU 2 outputs an ignition signal P for energizing and breaking a power transistor TR based on a crank angle signal SGT from a crank angle sensor 1. The power transistor TR energizes a primary current i1 at the time when the ignition signal P is a high level, and breaks the primary current i1 at the time when the ignition signal P is a low level.
At this time, a primary voltage Vi stepped up occurs in a primary winding 4a and thereby, a capacitor 9 is charged through a charging current path comprising a rectifying diode D1, a resistor R, the capacitor 9 and a rectifying diode D2. The charging of the capacitor 9 is completed at a point of time when a charging current of the capacitor 9 becomes equal to a reverse breakdown voltage (bias voltage VBi) of a Zener diode DZ.
The capacitor 9, the Zener diode DZ and the diode D2 form a bias section. charging is performed by a high voltage occurring in the low voltage side of the primary winding 4a at the time of breaking the primary current i1.
When the primary voltage V1 occurs in the primary winding 4a, a secondary winding 4b generates a secondary voltage V2 of several 10 kV increased as a high voltage for ignition. The secondary winding 4b applies the voltage to the spark plugs 8a to 8d of each of cylinders through the distributor 7 and generates a spark discharge in the spark plug of the cylinder targeted for ignition control to burn mixed gas.
When the mixed gas burns, an ion occurs inside a combustion chamber of a combustion cylinder so that an ion current i flows by the bias voltage VBi charged in the capacitor 9. The ion current i becomes an ion current detection signal Ei through a resistor 12.
A pulse generation circuit 20 generates and outputs a combustion pulse Fi to the ECU 2 only for a period during which the ion current detection signal Ei exceeds a threshold value. The ECU 2 determines whether the combustion cylinder of this time has burned or misfired based on that if a width of this pulse Fi is a predetermined value or more.
The ion currents detected in each of cylinders are combined and are inputted to the pulse generation circuit which is misfire detection section through one signal line. A detection period of the ion current is not limited in the related art. Therefore, there is a problem that a misfire detection signal, which is processed in a state where an ion current during an exhaust stroke of the previous cylinder is added to an ion current during a combustion stroke of a target cylinder, is transmitted and a misfire cannot be detected correctly.
FIG. 2 is a timing chart of the case that an ion current occurs to a combustion stroke of the next cylinder in a combustion state detection apparatus of a system according to the related art.
In FIG. 2, A is an ignition coil driving signal of each of cylinders. B is an ion current occurring in each of cylinders. C is a signal occurring in the Ei in the block diagram of FIG. 1. D is a signal occurring in the Fi in the block diagram of FIG. 1. In the present drawing, a third cylinder misfires and a first cylinder generates an ion current over a long time period. In a configuration of the example according to the related art, only one bias circuit is provided with respect to all the cylinders, so that the ion currents occurring in each of cylinders are added and are detected by an Ei portion. The ion currents detected by the Ei portion is subjected to a waveform shaping by the pulse generation circuit 20 and becomes the Fi. Therefore, when the ion current as shown in B occurs in each of cylinders, the Fi occurs during a combustion stroke of the third cylinder even though the third cylinder has misfired, so that a determination of combustion is made.
As described above, in the apparatus according to the related art, a bias voltage is applied from one bias circuit to the spark plug of each of cylinders through a high voltage diode and the ion currents of each of cylinders are detected and as a result, a signal in which the detected ion currents are added is obtained. However, since the ion currents may continue to occur to the exhaust stroke as well as the combustion stroke, in this configuration, there was a problem that, for example, even when the cylinder on detection has misfired, the misfire cannot be detected in the case that the ion current of the previous cylinder occurs over a long time and continues to the combustion stroke of the cylinder in question.
Also, when knock detection is performed by a vibration component superimposed on the ion current, there is a problem that a knock determination is made even when the cylinder in question does not cause a knock, for example, in the case that the previous cylinder similarly generates the ion current over a long time and noise vibration is included during the combustion stroke of the cylinder in question.
When the bias section and ion current detection section are provided every all the cylinders and an input signal to the ECU is also provided every the cylinder, such a problem does not arise, but it is necessary to increase a portion shared with plural cylinders as much as possible in order to achieve a reduction in cost and a reduction in the number of input signal lines.
According to an embodiment of the invention, there is provided a combustion state detection apparatus for an internal combustion engine including an angle sensor, an ECU, an ignition coil, a spark plug, a bias section, an ion current detection section, at least one of a misfire detection section and a knock detection section, at least one of a misfire determination section and a knock determination section, and a detection period limit section. The angle sensor detects a revolution angle of the internal combustion engine. The ECU performs fuel injection and ignition control based on revolution information from the angle sensor. The ignition coil generates a high voltage for ignition based on a driving signal from the ECU. The spark plug generates an ignition spark to ignite mixed gas by applying the high voltage for ignition of the ignition coil. The bias section applies a bias voltage for ion current detection to the spark plug. The ion current detection section detects an ion current. The misfire detection section performs misfire detection based on the ion current detected by the ion current detection section. The knock detection section performs knock detection based on the ion current detected by the ion current detection section. The misfire determination section and the knock determination section perform misfire determination and knock control based on an output signal of the misfire detection section and knock detection section, respectively. The detection period limit section limits a detection period of the ion current processed in the at least one of the misfire detection section and the knock detection section.
Even when an ion current on a combustion stroke of the previous cylinder reaches a combustion stroke of a target cylinder in a case of unifying the number of output signal lines to the ECU or sharing with plural cylinders, a detection period of the ion current is limited to a range of the combustion stroke of the target cylinder. Therefore, misfire detection or knock detection can be performed correctly.